Nucleoside analogues (NAs) are synthetic compounds structurally related to natural nucleoside. In terms of their structure, nucleosides are constituted by three key elements: (i) the hydroxymethyl group, (ii) the heterocyclic nitrogenous base moiety, and (iii) the furanose ring, which in several instances seems to act as a spacer presenting the hydroxymethyl group and the base in the correct orientation.
NAs are extensively used as antiviral and antitumor agents. These molecules have been traditionally synthesized by different chemical methods which often require time-consuming multistep processes including protection-deprotection reactions on the heterocyclic base and/or the pentose moiety to allow the modification of naturally occurring nucleosides (Boryski J. 2008. Reactions of transglycosylation in the nucleoside chemistry. Curr Org Chem 12:309-325). This time consuming multistep processes often lead to low yields and increased costs. Indeed, chemical methods usually increase the difficulty of obtaining products with correct stereo- and regioselectivity, generating secondary products (Condezo, L. A., et al. 2007. Enzymatic synthesis of modified nucleosides, p. 401-423. Biocatalysis in the pharmaceutical and biotechnology industries. CRC Press, Boca Raton, Fla., Mikhailopulo, I. A. 2007). Moreover, the chemical methods include the use of chemical reagents and organic solvents that are expensive and environmentally harmful.
Since several non-natural nucleosides acting as antiviral or anticancer agents have modifications on their sugar moiety, it is interesting to explore the possibility of developing a novel and effective industrial biocatalyst to catalyze the enzymatic synthesis of nucleosides analogues i.e. to develop a synthesis of active pharmaceutical ingredients (APIs) or their intermediates which can be applied on an industrial scale.
Surprisingly, it was found that the drawbacks of previous cited chemical synthesis routes can be avoided and NAs can be obtained with a conversion higher than 50% and/or an anomeric purity higher than 95%. That is possible based on the use of Nucleoside Desoxyribosyl Transferase (NDT or NdT) enzymes that we claim in the present invention.
The advantages of the NDT bioenzymatic synthesis are:                (i) One-pot synthesis,        (ii) Reduced number of steps,        (iii) Higher conversions and yields,        (iv) Avoidance of organic solvents in the enzymatic step,        (v) No protection/deprotection strategies, e.g. for the hydroxyl groups in the sugar, are needed,        (vi) Mild reaction conditions: environmentally-friendly technology (water or aqueous medium, neutral pH),        (vii) Extremely good selectivity: stereoselectivity—enantioselectivity, chemo-regioselectivity,        (viii) Fewer or no side reactions: impurity profile (reduced by-products content),        (ix) Reduction in overall waste generation,        (x) Process productivity,        (xi) Overall lower cost of production        